Method of electroplating metal



June 16, 1936.

c. A. HARRISON METHOD OF. ELECTROPLATING METAL Filed March 5, 1932 2Sheets-Sheet 1 "XA/M XX Mm N/WMX/ INVENTOR @MMI Vm A TTORNEYi C. A.HARRISON METHOD- OF ELECTROPLATING METAL June 16, 1936.

Filed Marh 5, 1932 2 Sheets-Sheet 2 INVENTOR BY 1 lewifiari'iiwa,

' m ATTORNEY! Patented June 16, 1936. I

UNITED STATES;

2,044,431 7 METHOD or ELECTROPLATING METAL Charles-A. Harrison,Lockport, N. 'Y., assignor to Anaconda Copper-Mining Company, New York,N. Y., a corporation of Montana Application March 5, 1932, Serial r:597,027

Claims.

The present invention relates to a method of and apparatus forcompletely coating an article or object with a uniform deposit of metal,and more particularly to a method wherein the complete and uniformcoverage or deposition'is produced by electrodeposition.

It has been well known in the plating art that a coating produced uponan object by electrodeposition is in general not of uniform depth or 10thickness throughout the total surface of the object covered, but thatthe depth of the coating or plating upon certain portions of the objectis of materially greater depth or thickness than at certain otherportions; this increase in thickness or build-up is particularlynoticeable upon the edges or extremities of the object being coated.

Where maximum cathodic current densities are used commensurate with theformation of a so smooth coherent deposition of metal upon themid-portion of the cathode or object to be plated, the edge portions orextremities are'found to be plated or coated with a non-coherent,dendritic,

or crystalline deposit, or an excessive quantity of 25,metal forming orproducing a bulbous effect at these portions. Although this effect isproduced upon the extremities of most materials subjected to cathodicdeposition, it is more particularly disadvantageous in the plating ofcertain types of work, as for instance in the coating of cores in theproduction of radiator units wherein the build-up on the edges isparticularly disadvantageous.

Several attempts have been made to overcome this particular difliculty,all of which have resulted in butindifierent success. It has beenproposed to protect the edge portion of the object to be plated with anon-conducting shield or shroud. This'type of operation has not elimi-40 nated the difilculty as the, build-up upon the extremities is merelyspread out over a larger area. Other suggestions have been broughtforward but none of them comprehend a plating method whereby the totalsurface of the finished product is provided with a coating. Thus, it hasbeen proposed to cut oil" that portion of the object upon which thebuilt-up deposit has accumulated or, to obtain the same effect bycoating the extremitie's of the object to be plated with a metallicenclosure, plate this composite electrode, and after the platingoperation, remove the metallic enclosure with the built-up portionthereon. These latter methods, of course, leave the extremities uncoatedand in many types of work this particular operation is of no avail since(Cl. 204-6) it is desired to coat the entire exterior surface withmetal.-

The present invention, therefore, comprehends a method of coating theentireexterior surface of theobject to be plated and at the same time,avoid the disadvantageous build-up which is normally encountered uponthe extremities of such objects. This and other objects of the inventionwill be more clearly understood from the following description and willbe pointed out with particularity in the claims appended hereto.

In the drawings:

Fig. 1 is a cross section through a plating bath in which is shown acathode arrangement for use with my method of plating.

Fig. 2 is a fragmentary plan view of the invention.

Fig. 3 is a fragmentary perspective of the invention.

Fig. 4 is an enlarged fragmentary transverse section'showing thedisposition of an anode and cathode.

Fig. 5 is an enlarged fragmentary drawing of the cathode frame.

Fig. 6 shows another mode of connecting the object to be plated and theframe in electrical contact.

V Fig. 7 shows another form of electrical connection. I

A containerfor an electrolytic bath is shown generally at III made ofany desirable composition depending upon the type of electrolyte in thebath and upon the temperature at which the bath is maintained. Thecontainer is equipped with the usual means for conveying current to andfrom the bath, as for instance the bus bars II and I3 with whichelectrical contact is made to supply electrical energyto the electrodes.The support member I2, having electrical contact with the bus bar I I,is provided to support an electrode such as the cathode I 5 and to leadelectrical energy to it. Another main line or .bar I3 is provided forelectrical contact with the support bar I2 which supports the otherelectrode of the cell, as for instance the anode I 4, (Fig. 2).

The cathodic portion is hung from bar I2 into the electrolytic bath I6by means' of the hooked strapmembers I8 while the anode is hung from barI2 by the hooked members I9.

The material or object to be plated as cathode I5, is'connected inelectrical contact with the source of current through the supportingmember I2 resting upon bus bar. I I, the object I5 serving as a cathodeof an electrolytic cell. Upon passage of current through a suitableelectrolyte trically'conducting member which is adjacent containedwithin the cell, metallic material is deposited upon the cathode anddepending upon electrically conducting member at the cathode potentialwhereby current flowing from the anode to the cathode will flow boththrough the object to' be plated and through the additional electheextremities of the object to be plated and spaced therefrom at apredetermined distance. Thus, a frame member 20 surrounds the object tobe plated or cathode, that is, the cores or grids l5, and is spaced fromthe grids a predetermined distance. 15 and the frame 20 since they arein electrical contact with the supporting member l2, and therefore thesemembers have the same electrical potential with respect to the anode.

It will be noted that so long as the frame is at exactly cathodepotential, metal will be plated from the bath upon the cathode or gridsl5 and the auxiliary, electrically conducting member, that is the framemember 20, simultaneously. Should, however, the frame member be heldslightly more positive than the cathode, that is, positive with respectto the cathode in the same 'sense that the anode is positive withrespect to the cathode in potential between that of the anode andcathode but nearer in value to the latter, the frame is going to receivemetal but as it is slightly positive with respect to the cathode it willplate copper to some extent upon the cathode. On the other hand shouldthe frame be held more negative than the cathode, metal would depositboth upon the cathode and the frame while metal would be plated upon theframe from the cathode.

In-a condition of operation which I desire to obtain, I maintain theauxiliary electrically con ducting frame member 20 at a potential whichis substantially cathode potential and thereby cause metal from theanode H to pass into solution in the electrolyte l6 and deposit out uponboth the grid i5 herein, and upon the auxiliary electrically conductingframe member 20 and prevent any excessive build-up of plated. metal uponthe edges or extremities of the object to be plated, in this instancethe grids l5. By so conducting the plating I have made it possible toprevent the excessive build-up upon the edges of the article, and infact have been able to plate the metal more rapidly upon the framemember than upon, the edges, or even to remove metal from the edges ofthe cathode and cause the plating at these points to be of less depth orthickness than the plating upon the main portion or mid-portion of thecathode.

In Fig. 4 anodes are indicated at I4 and the cathode at IS with anelectrically conducting frame member 20, also at cathode potential,placed adjacent the extremities of the'cathode l5 and spaced apredetermined distance therefrom. The passage of the electric current isindicated generally by means of arrows and is shown as Current flowsthrough both the grids passing in substantially straight lines from theanode to the cathode at the mid-section of the cathode while the currentis shown flowing in bowed or arcuate lines from the anode to theextremities of the portion at cathode potential with deposition of largequantities of metal I! at the portions adjacent the edges or extremitiesof the portions acting as true cathode, that'is, the cathode grid l5 andframe 20. It is readily seen, therefore, that the inter-position of theframe member 20 adjacent the edge portions or extremities of the cathodewill receive the bowed or arcuate portion of the current or that portionof the current which causes the excessive buildup of metal at this pointon the cathode and will thereby shield the extremities of the cathodeand prevent the formation of loose and flocculent deposits, or ofdendritic deposits.

In Figs. 6 and 7 is shown a disposition of frame member 20 and cathode[5 wherein these members are not in contact but wherein the members l5and 20 have electrical contact with the support bars [2 and 30. strapmember 26 from the supporting bar I2 and the frame 20 by an independentstrap member 27 from the bar 30 thus avoiding contact be tween the frame20 and the cathode l5.

In order to obtain a variation of the potential existing between theanode M and the cathode grid l5 and the. anode and the frame member 20,an auxiliary control generator of the type indicated in Fig. 6 at A. G.is inserted in the line between the main plating generator P. G. and theframe member 20. By a suitable choice of such generator the frame 20 maybe made either positive or negative with respect to the grid l5.According to the hook up in Fig. 6 the anode I4 is connected in the linethrough the bus bar [3, (not shown) and the grid: I5 to bus bar ll,electrical contact being made with the frame member 20 from theauxiliary generator A. G. It is to be noted that the frame 20 and gridl5 are spaced from one another and that a supplemental support bar 30 isused from which the frame 20 is suspended by the hooked strap member 21,the

bar 30 being insulated from the bus bars l3 and tor P. G. and hencethere is a difference of po-,

tential not only between the anode l4 and the cathode [5, but betweenthe cathode i5 and the frame 20; By cutting out the resistance V. R. theelectrical hook-up then becomes essentially the same as indicated in thefigures other than Fig. 6 and Fig. 7 where there is the same potentialexisting between anode l4 and cathode l5 as between anode l4 and frame29.

It is to be noted that throughout the several views the support bars l2and I2 are indicated as being provided with an insulated end, as at 32,so that these bars may be the-more readily supported by suspending themtransversely of the plating tank and supporting them upon the bus barsII and I3.

The cathode I5 is hung by The auxiliary electrically conducting framethat a U or channel shaped member of stainless steel provided with anon-conducting core 25 is suitable since the exterior of the framemember of this composition is not prone to rust or deteriorate due tothe action of the chemical Imaterials which may be contained in theelectrolytic bath. Further, such a frame member may be specially treatedupon the conducting exterior thereof in order to' prevent too greatadherence between the deposited metal and the metal of the frame memberby coating the exterior of the frame member with a suitable chemicallyinert substance such as vaseline or high boiling hydrocarbon oil orgrease. The deposited metal may be removed readily from the frame ashighly purified material and used as such.

It will be seen that the invention efiectively protects the extremitiesof an object to be plated from the build-up which is normallyencountered in electrolytic plating but permits the deposition of asubstantially uniform depositupon the entire surface of the object inone operation.

What is claimed is:

1. The method of plating an object with metal uniformly byelectrodeposition which comprises attaching the object as an electrodeto a source of current, immersing the object in an electrolyte andplacing an electrically conducting member at the extremities of theobject, said member being spaced from the object and having a potentialless than the cathode potential.

2. In a metal plating operation the method of controlling the plating ofan object over a predetermined area thereof which comprises attachingthe object as a cathode to a source of current whereby metal deposits onthe object, immersing the object in an electrolyte and placing anelectrically conducting member adjacent the portion of the object wherethe plating is to be controlled, said member being spaced from theobject and having a cathode potential less than the poten tial of thecathode and plating metal from the anode upon the object and saidmember.

3. The method of depositing upon an object by electrodeposition a layerof metal of substantially uniform thickness which comprises immersingthe objectin an electrolyte in a cell containing an anode, connectingsaid object to a source of cur- 5 rent to act as cathode in the cell,placing an electrically conducting member at the extremi ties of saidobject and out of the direct path of current flow from the modem theobject through the electrolyte, said member being out of electricalcontact with said object, and maintaining said member at a potentialless than the cathode potential of said object.

4. In a metal plating operation, the method of controlling thedeposition of metal on a predetermined area of an object, whichcomprises immersing the object in an electrolyte in a cell containing ananode, connecting said object to a source of current to act as cathodein said cell, placing an electrically conducting member adjacent saidarea on said object and out of the direct path of current flow from theanode to said area through the electrolyte, said member being out ofelectrical contact with said object, maintaining said member at apotential less than the cathode potential of said object, andwithdrawing current from the cell both through said object and throughsaid member to cause metal to be deposited on both said object and saidmember. 30

5. The method of depositing upon an object by electrodeposition a layerof metal of substantially uniform thickness which comprises im-' mersingthe object in an electroLvte in a cell containing an anode, connectingsaid object to a 35 sourceof current to act as cathode in the cell,placing an electrically conducting member at the extremities of saidobject and out of electrical contact with said object, and maintainingsaid member at a potential less than the cathode potential of saidobject.

- CHARLES A. HARRISON.

